4" Flat BW CRT , can't flip image vertically

[samu]

Hi ,
I'm working on a project that will use one of those 4 inch B/W CRTs sold on aliexpress that were made for Chinese door phones.

It works great normally, but my project requires that I mount the CRT upside down and flip the video vertically (like is done in the 4" sony watchman models). I know that this is usually done by swapping the vertical yoke connectors. I swapped my vertical leads, which had a resistance of 15.1 ohms between them while the other two (horizontal deflection) leads had a resistance of 2.2 ohms.

However, this produces a completely white screen with no discernable image, and no amount of fiddling with pots has changed this. Moving pots around (vert/horiz size/position etc.) randomly does sometimes produce some change, but only in that the purely white screen sometimes gets darker in certain areas.

Movement in the video input is discernable, for example when changing menu screens in a game, a dull sweeping movement can be made out. It almost seems like the image is just extremely out of focus, to the point where the entire screen is just displaying a white mass and only movement is sometimes discernable. Still, adjusting the focus pot does nothing.

Swapping the vertical leads back and swapping the horizontal leads instead produces the desired horizontal mirrored effect with no problems, but this isn't what I need.

I guess it has something to do with the weird angle that a flat CRT like this is forced to project at.

Has anyone had any experiences with something like this? Any ideas of what I can do to fix it? Unfortunately software is not an option. I'm new to CRTs, sorry if I'm missing something.